- Based on comments from #974, follow the configuration
scheme from services-systemd, so with separate lists
"services" and "disable". This ties it **slightly**
less closely to the commands passed to rc-config.
- If runlevel isn't set (at all) then use "default". For
most systems that do not use multiple runlevels, this
simplifies the configuration to just a list of service names
to add or delete.